Mystery Fungus Ravages North American Bat Populations

Scientific community scrambles to understand the frightening plague and formulate a cure

Bats in the eastern U.S. are now facing what could be their biggest challenge, with hundreds of thousands reported dead by the U.S. Fish and Wildlife Service and many species heading toward extinction.

Dead and dying bats were first discovered three years ago in caves near Albany, N.Y., appearing to suffer from an inexplicable white fungus originating around their noses, ears, wing membranes, and occasionally tails. The affliction, later dubbed White-nose Syndrome (WNS), had not previously been documented in the U.S. Thriving in the cold conditions of bat hibernacula, which include the caves, sinkholes, mines and other areas where bats hibernate during the winter, the baffling syndrome has quickly spread across nine states from New Hampshire to Virginia in only a few years.

At a Congressional hearing on WNS in June, Merlin D. Tuttle, Ph.D., Founder and President Emeritus of Bat Conservation International, submitted testimony on the disease: "At the current rate of spread, the most critical hibernation sites for federally endangered Indiana bats, gray bats, Virginia big-eared bats and Ozark big-eared bats will face WNS within two years or less, and several additional bat species may warrant consideration for Endangered Species [Act] listing."

Last May, Dr. Tuttle and other prominent scientists and wildlife managers concerned about WNS formulated a consensus statement that declared, WNS "is a devastating disease of hibernating bats that has caused the most precipitous decline of North American wildlife in recorded history. Since it was first discovered in 2006, WNS has infected six species of insect-eating bats in the northeastern and southern U.S., causing declines approaching 100% in some populations…".

Unfortunately, little is known about WNS. Scientists have not been able to discover the direct cause of mortality. According to Tuttle, it is also unknown if the fungus of the genus Geomyces is the singular cause of death or simply "an opportunistic pathogen that takes advantage of weakened immune systems."

What is certain, however, is that many of the one million infected bats who have already died seem to have starved to death. Scientists discovered that the bats awaken prematurely from their hibernation and appear to seek out prey in mid-winter. Often unable to find insects otherwise available in warmer months, the bats’ bodies are forced to use energy from fat reserves intended for use during hibernation. The infected bats are commonly found with necrotic and ulcerated wing membranes and compromised immune responses, exhibiting atypical behavior, such as flying during the day or flapping around erratically on the ground.

No longer simply stigmatized as the villains of horror movies or childhood nightmares, bats are now known to be valuable assets to agriculture and the environment as insect consumers and pollinators. They comprise approximately a quarter of all mammal species on the planet, 70 percent of which are insect predators. Bat species prey on insects that damage crops, as well as those that can destroy forests or spread disease; some bats are even known to eat up to 600 mosquitoes in an hour. Many scientists fear the mass bat mortalities will contribute to increased pesticide use, poor forest health, and increased risk of insect-borne diseases.

At the Congressional hearing, House Chairwoman Madeleine Bordallo (D-Guam) stated, "We must quickly ascertain the causes of and vectors for the spread of White-nose Syndrome to avoid what could be an ecological and economic disaster, if it remains unchecked."

Researchers have stressed that the top priority must be understanding WNS and its means of spreading if they ever hope to find a cure. Scientists made clear at the Congressional hearing that more than a quarter of the 46 bat species in the U.S. may need to be listed under the Endangered Species Act, and some of even the most abundant and widespread species could swiftly become threatened with extinction.